You'll first need to move the darenet.pem file you created to your ~/.weechat/certs directory:
mv darenet.pem ~/.weechat/certs
Now, if you have already connected, disconnect and remove the current DareNET server(s). Re-add it using the following commands:
/server add darenet irc.darenet.org/6697
/set irc.server.darenet.ssl on
/set irc.server.darenet.ssl_cert %h/certs/darenet.pem
/set irc.server.darenet.ssl_dhkey_size 2048
and then reconnect to DareNET
/connect darenet
Once done, read how to add your certificate's fingerprint to N.